ELECTRONIC AND ELECTRICAL FUNDAMENTALS

Section A

Attempt all the questions in this section (50 marks)

1.

Convert the following numbers.

(

a

)

Binary to Decimal

11101001

2

(

b

)

Hexadecimal to Binary

E4

16

(

c

)

Decimal to Hexadecimal

215

10

2.

Identify the circuit symbols shown in Figure Q2(

a

) and Figure Q2(

b

).

(

a

)

Figure Q2(

a

)

(

b

)

Figure Q2(

b

)

3.

Determine the logic input X and Y for the gates shown in Figure Q3(

a

) and

Figure Q3(

b

) respectively.

(

a

)

X

1

1

Figure Q3(

a

)

(

b

)

0

Y

0

Figure Q3(

b

)

4.

Figure Q4 shows a current carrying conductor placed between magnetic poles.

The magnetic flux density is 0·2 Tesla. The conductor experiences a force of 1·2

N

when the current is 15

A.

N

S

Figure Q4

(

a

)

Determine the length of conductor within the magnetic field.

(

b

)

State what happens to the force when the current direction is reversed.

5.

Referring to Figure Q5, and using the supplied datasheet:

V

IN

330

?

RED

LED

L424 HDT

Figure Q5

(

a

)

state the purpose of the series resistor;

(

b

)

state the maximum forward current the diode can handle;

(

c

)

state the typical forward voltage drop;

(

d

)

determine the maximum value of input voltage that can be safely applied.

6.

A generator produces a sinusoidal current represented by the equation

i

= 12sin

?

amperes

Determine:

(

a

)

the maximum value of the current;

(

b

)

the r.m.s. value of the current;

(

c

)

the average value of the current;

(

d

)

the instantaneous value of the current when

?

= 30°.

7.

With reference to the circuit shown in Figure Q7, in which resistor R

1

is 10

k

?

and

R

V

can be varied between 5

k

?

and 15

k

?

:

V

0

100

mV

R

1

R

V

Figure Q7

(

a

)

name the circuit configuration;

(

b

)

determine the output voltage when R

V

is set to 10

k

?

;

(

c

)

determine the maximum possible output voltage when the input is 100

mV;

(

d

)

determine the minimum possible output voltage when the input is 100

mV.

8.

With reference to the circuit shown in Figure Q8:

3

?

2

A

10

?

18

V

12

V

R

Figure Q8

(

a

)

determine the voltage across the 3

?

resistor;

(

b

)

determine the current through the 10

?

resistor;

(

c

)

determine the value of resistor R.

(

d

)

A fault condition causes the 10

?

resistor to be open circuit. Determine the

new value of supply current.

9.

For the circuit shown in Figure Q9:

A

B

C

Z

Figure Q9

(

a

)

determine the Boolean expression for output Z;

(

b

)

draw the truth table for the circuit;

(

c

)

determine the circuit output Z when a faulty condition causes the output of the

invertor to be permanently low (logic 0).

[Turn over for Section B on

Section B

Attempt any TWO questions in this section (50 marks)

Each question is worth 25 marks

10.

(

a

)

State the logic output for the logic gates shown in Figure Q10(

a

)(i) and

Figure Q10(

a

)(ii).

(i)

1

0

Z=

1

Figure Q10(

a

)(i)

(ii)

1

0

Z=

1

Figure Q10(

a

)(ii)

(

b

)

Add the following binary numbers.

(i)

0101

2

+ 0101

2

(ii)

0010

2

+ 0101

2

(

c

)

Draw the logic circuit for the expression

Z = A.B + A

¯

.C

(

d

)

Determine the logic expression for the logic circuit shown in Figure Q10(

d

).

A

Z=

B

A

C

=

1

&

=

1

Figure Q10(

d

10.

(continued)

(

e

)

Figure Q10(

e

)(i) shows a logic circuit.

1

R

S

T

4

2

5

Z=

3

Figure Q10(

e

)(i)

(i)

Determine the logic expression for the circuit.

(ii)

Draw the truth table for the circuit.

(iii)

The circuit shown in Figure Q10(

e

)(i) has developed a fault, and upon

testing the outputs shown in the truth table Figure Q10(

e

)(iii) were

obtained. Explain which gate (input or output) is at fault and state the

nature of the fault.

R

S

T

Z

0

0

0

1

0

0

1

1

0

1

0

1

0

1

1

0

1

0

0

1

1

0

1

1

1

1

0

0

1

1

1

0

Figure Q10(

e

)(iii)

11.

(

a

)

For the circuit shown in Figure Q11(

a

), determine:

R

1

1

A

8A

V

S

2

A

20

A

R

3

R

5

R

6

R

7

R

4

R

2

Figure Q11(

a

)

(i)

the current flowing in R

3

;

(ii)

the current flowing in R

6

.

(

b

)

For the circuit shown in Figure Q11(

b

), determine:

R

1

1

A

10

?

20

?

10

?

20

?

V

S

4

A

3

A

R

3

R

5

R

6

R

7

R

4

R

2

Figure Q11(

b

)

(i)

the voltage drop across R

7

;

(ii)

the supply voltage;

(iii)

the power dissipated in R

7

;

(iv)

the energy consumed in 3 hours by the branch containing R

2

& R

4

.

(

c

)

A variable speed, 10

kW generator produces an output voltage of 120

V, has a

flux density of 40 milliTesla, and a conductor length of 25

m. Calculate:

(i)

the speed of the generator;

(ii)

the speed of the generator when the output voltage is 200

V;

(iii)

the maximum current the generator can supply when the output is 200

V.

(

d

)

A conductor is forced to move downwards within a magnetic field, as shown in

Figure Q11(

d

).

N

S

Figure Q11(

d

)

(i)

State the formula used to calculate the current in the conductor.

(ii)

Explain how the direction of the current can be determined.

12.

(

a

)

For the circuits shown in Figures Q12(

a

)(i) and (ii) the input voltage is

12

V

pk–pk

, 50

Hz in each circuit.

(i)

Assuming that the switch remains open, sketch the input and output

waveforms for the circuit shown in Figure 12(

a

)(i), clearly indicating the

differences between the input waveform and the output waveform.

D1

C1

V

OUT

12

V

pk–pk

R

L

Figure Q12(

a

)(i)

(ii)

Sketch the output waveform for the circuit shown in Figure 12(

a

)(ii),

clearly indicating the differences between the new output waveform and

the output waveform of Figure Q12(

a

)(i).

D1

12

V

pk–pk

D4

R

L

D2

D3

Figure Q12(

a

)(ii)

12.

(continued)

(

b

)

For the circuit shown in Figure Q12(

b

):

R

v

R

i

V

IN

=

2

V pk–pk

R

f

=100

K

V

OUT

5

Circuit

Gain = -5

1

Figure Q12(

b

)

(i)

state the circuit configuration;

(ii)

determine the output voltage;

(iii)

determine the value of R

i

;

(iv)

explain the purpose of R

v

.

(

c

)

(i)

Identify the circuit shown in Figure Q12(

c

).

(ii)

With reference to Figure Q12(

c

), identify the purpose of each of the

following components: R

1

& R

2

, C

2

& C

3

.

R

1

Ideal

Transistor

Gain = 500

R

3

C

2

1K5

I

C

R

2

R

4

C

3

6K8

1·4

V

6

V

0

V

V

CC

12

V

C

1

Figure Q12(

c

)

(iii)

Calculate the output voltage for the circuit shown in Figure Q12(

c

) when

the input voltage is 20

mV

pk–pk

.

[Turn over for Question 12(c) continued on

12.

(

c

)

(continued)

(iv)

When the input voltage is increased to 40

mV

pk–pk

the output waveform

is as shown in Figure Q12(

c

)(iv).

V

OUT

+6

V

-6

V

0

V

t (secs)

Figure Q12(

c

)(iv)

Explain why the shape of the waveform is non-sinusoidal.

(v)

Suggest two ways of preventing this.

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